Here are quotes from the article "How to Make Music on Your Smartphone", featuring IK's iRig MIDI 2:
"Sometimes it's not the sound of a traditional instrument, but the feel that a musician's after. That's why MIDI keyboards, controllers and other devices are also popular among home recordists. A device like the IK Multimedia iRig MIDI 2 allows you to hook up an actual MIDI keyboard to your phone. You can then translate the result into a track in GarageBand or another music app."
Learn more about controlling music creation apps, using MIDI controllers and making music on your smartphone with iRig MIDI 2.